Elongated items such as power cables, wiring bundles or optical fiber cables used for telephone, video or computer communication networks are often installed in protective conduit which may be buried underground, strung from support stanchions or positioned within building structures along with other utility and service lines. Such conduit may be, for example, extruded polymer tubes which provide substantially continuous protection to the elongated items from moisture, abrasion, impact and other environmental hazards.
Once the conduit is in place, for example, underground or throughout a building structure, it is difficult to position cables within it because the interior of the conduit is accessible only at isolated node points where the elongated items are connected to components or where splices are effected. Installation of cables and other items is accomplished by drawing the items through the conduit between nodes. The conduit may be long and typically does not follow a straight path, and due to the weight of the elongated items and the tortuous path they must follow, drawing of the items through the conduit requires considerable tensile force.
It is further advantageous to pre-position a plurality of protective sleeves within each conduit in preparation for installation of the elongated items. Each protective sleeve receives an elongated item within an interior space, the item being drawn through the sleeve within the conduit. The sleeves protect the elongated item from abrasion as they are being drawn through the conduit during installation. The sleeves also protect the elongated items from abrasion from other items being drawn through the conduit and provide for efficient use of the conduit interior, allowing elongated items to be organized and separated from one another.
Protective sleeving may be woven from polymer filamentary members to ensure flexibility and toughness. Each sleeve preferably has a pull tape pre-installed within its interior space. The pull tape is used to draw an elongated item through the sleeve for installation of the item within the conduit. In the installation operation, one end of the pull tape is attached to the elongated-item, and the opposite end is manually pulled or attached to a power winch that draws the pull tape, and the elongated item attached thereto, through the sleeve and thereby through the conduit in which the sleeve is positioned.
Pull tapes must withstand significant tensile stress and yet remain flexible so that they can readily comply with the shape of the conduit in which the pull tape is positioned. To provide for high tensile strength as well as flexibility, it is found advantageous to weave or braid the pull tapes from high strength yarns. However, it is found that woven or braided pull tapes encounter significant friction as they are drawn through the protective sleeve within the conduit. The friction between the pull tape and the sleeve increases the force needed for the pull, thus, increasing the chances of a pull tape parting and decreasing the maximum length over which a pull can be effected. Furthermore, it is known that the pull force required to draw a pull tape through a conduit increases geometrically as the number of bends in the conduit increases. Thus, if a conduit run has too many bends, it may not be feasible to draw a pull tape through it because the pull force required for the draw may exceed the tensile limit of the tape. It would be advantageous to mitigate the friction between the pull tape and the sleeve to lower the pull force and thereby decrease the chance of pull tape failure and increase the maximum distance and the number of bends over which an item may be drawn.